New Microchips Shun Transistors

For the first time, researchers have created a working prototype of a radical new chip design based on magnetism instead of electrical transistors.

As transistor-based microchips hit the limits of Moore's Law, a group of electrical engineers at the University of Notre Dame has fabricated a chip that uses nanoscale magnetic "islands" to juggle the ones and zeroes of binary code.

Wolfgang Porod and his colleagues turned to the process of magnetic patterning (.pdf) to produce a new chip that uses arrays of separate magnetic domains. Each island maintains its own magnetic field.

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Because the chip has no wires, its device density and processing power may eventually be much higher than transistor-based devices. And it won't be nearly as power-hungry, which will translate to less heat emission and a cooler future for portable hardware like laptops.

Computers using the magnetic chips would boot up almost instantly. The magnetic chip's memory is nonvolatile, making it impervious to power interruptions, and it retains its data when the device is switched off.

The magnetic architecture of the chip can be reprogrammed on the fly and its adaptability could make it very popular with manufacturers of special-purpose computing hardware, from video-game platforms to medical diagnostic equipment.

"The value of magnetic patterning in storage devices such as hard drives has been known for a long time," said Porod, Freimann professor of electrical engineering at the University of Notre Dame. "What is unique here is that we've applied the patterning concept to the actual processing."

The chip's nanomagnets — on the order of 110 nanometers wide — can be assembled into arrays that mirror the function of transistor-based logic gates in addition to storing information. These logic gates are the building blocks of computer technology, giving microchips the power to process the endless rivers of binary code.

A NAND logic gate, for example, accepts two inputs to arrive at one output. If both inputs are one, the NAND gate spits out a zero. If one or the other or both inputs are a zero, the NAND gate provides a one as an output.

Porod and his colleagues equipped their new chip with a universal logic gate — a combination of the NAND and NOR gates. Together, these two logic gates can perform any of the basic arithmetic functions intrinsic to all computer processing.

This exotic method of transistorless processing — known as magnetic quantum cellular automata — originally used individual electrons as quantum dots, arranged in a matrix of cells to handle logic operations. But nanoscale magnets proved to be a much better alternative because they were not subject to stray electrical charges, and they were easier to fabricate.

"The magnets were created from ferromagnetic nickel/iron alloy," said Porod. "We evaporated a thin layer of the alloy onto a silicon surface, then patterned the islands using electron-beam lithography."

Logic operations within the processor commence with a pulsed magnetic field on the input magnet, which alters the orientation of its magnetic field. This creates a cascade effect across the array, as magnetostatic attraction and repulsion cause the fields of adjacent magnets to "flip."

"To read the output, we used a scanning probe to infer what the magnetization was," said Porod. "Ideally, in the future, we would like to achieve this (input and output) with the simple application of an electric current."

Although existing technologies use magnetic fields to store information on small chips called MRAMs, this is the first application to produce a chip that can process digital information in addition to storing it.

The potential of chips driven by nanoscale magnets was considered five years ago at London's Imperial College. Professor of nanotechnology Russell Cowburn and his colleagues observed that the magnets could exchange information as their fields interacted with each other.

Cowburn is encouraged by the technological leaps made at the University of Notre Dame. "What's really exciting here is that you can implement all of the Boolean functions without using a single transistor," he said.

The new chips also have some important characteristics that might make them ideal candidates for use in future space hardware. "You can't just put a regular DRAM into space, because it won't tolerate the environment. The magnetic technology is radiation-hard, and will be a huge improvement on what they're using now," Cowburn said.

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